Method of making known and previously unavailable pyrylium salts

ABSTRACT

A method is disclosed for preparing pyrylium and thiapyrylium salts having the formula represented below (where X is O,S or Se): ##STR1## and where R 1  and R 2  represents a branched or unbranched alkyl radical having up to about 15 carbon atoms, an aromatic group having as substituents alkyl radicals with 1 to about 15 carbon atoms, alkoxy radicals having 1 to about 4 carbon atoms, substituted amino radicals have 1 to 2 carbon radicals containing 1 to about 4 carbon atoms, a heterocyclic group having as substitute alkyl radicals with 1 to about 15 carbon atoms, alkoxy radicals having 1 to about 4 carbon atoms and amino radicals having 1 or 2 carbon radicals containing 1 to about 4 carbons, thiophene radicals and furan radical containing a variety of substituents; R 3  represents a thioalkyl radical having 1 to about 4 carbon atoms thiobenzyl, thioaryl and thiocycloalkyl, as well as thiohetaryl radicals such as thiohydridyl and related 5-and 6-membered systems; and Z -  is an anionic function. The salts are prepared by condensing the methyl ketone with carbon disulfide in the presence of sodium hydride, treating the product with methyl iodide to form the α-oxoketenedithioacetal; condensing the α-oxoketenedithioacetal with another methyl ketone in the presence of two equivalents of potassium tert-butoxide to form a 1,5-enedione; and cyclizing the enedione with tetrafluoroboric acid.

FIELD AND BACKGROUND OF THE INVENTION

The disclosed invention is a simplified method of producing known andpreviously unavailable pyrylium, thiopyrylium, and seleninium salts. Themethod produces those types of salts which have a displaceablesubstituent in the 4-position which allows the attachment of such salts,by displacement of this group, to a variety of organic substrates orsupports. The process utilizes readily available starting materials andreaction conditions which are suitable for industrial scale use. Afeature of the method and the salts produced by the method is theincorporation in the 4-position of the pyrylium and thiopyrylium salts,of a group readily displaceable by nucleophiles. This permits theattachment of the salts to an inert organic polymeric support such ascross-linked polystyrene.

Pyrylium salts are used in commercial photocopying devices and thus havewide spread application.

It is known that such salts enhance the efficiency and effectiveness ofphotoconductive compositions. See U.S. Pat. No. 3,938,994 to Reynolds etal; U.S. Pat. No. 3,615,396 to Gramza et al; and U.S. Pat. No. 3,250,615to Van Allan et al.

Various techniques are known for the preparation of pyrylium and relatedsalts. Such techniques are related to methods of preparing a largerclass of substituted pyridines which contains the class of pyryliumsalts.

Among the numerous ways to prepare substituted pyridines described inthe literature, [see Klingsberg, E., "The Chemistry of HeterocyclicCompounds. Vols. I-III. Pyridine and its Derivatives," IntersciencePublishers, New York, 1960 and Abramovitch, R., "The Chemistry ofHeterocyclic Compounds. Supplement to Pyridine and its Derivatives."Wiley-Interscience, New York, 1978] a noteworthy example is the use oforganolithium compounds for the preparation of arylpyridines [seeZiegler, L.; Zeiser, H. Ber., 1930, 63, 1847; Overberger, G. C.;Lombardino, J. G.; Hiskey, R. G. J. Amer. Chem. Soc. 1957, 79, 6430;Bryce, D.; Skinney, A. C. J. Chem. Soc. 1963, 577], 2,2'-dipyridinyls[see Newkome, G. R., Hager, D. C., J. Amer. Chem. Soc. 1978, 100, 5567;Parks; J. E.; Wagner, B. E.; Holm, R. H. J. Organomet. Chem. 1973, 56,53] and 2,2',2"-terpyridinyl [see Kauffman, T.; Konig, J.; Woltermann A.Chem. Ber. 1976 109, 3864] and the application of pyridiniumphenacylides or their salts in the synthesis of a wide variety of2,4,6-trisubstituted pyridines [see Krohnke, F. Synthesis 1976, 1;Tewari, R. S.; Misra, N. K.; Dubey, A. K. J. Heterocyclic Chem. 1980,17, 953 and earlier references]. This last procedure has been applied tothe synthesis of numerous substituted di-, tri-, quater-, quinque-,sexi- and septipyridinyls, all of which are of interest as ligands formetal chelation. 2,2'-Di- and 2,2',2"-terpyridinyl have attracted themost attention in this respect [see Wilkins, C. J.; Douglas, J. E.Inorg. Chim. Acta, 1969, 3, 635], and the 4'-(4-methoxyphenyl)terpyridinyl [see Deggau, E.; Krohnke, F.; Schnalke, K. E.; Staudinger,H. J.; Weiss W., Z. Klin. Chem., 1965 3, 102; Stamm, D.; Staudinger, H.J.; Weiss, W. ibid. 1966, 3, 222], and its sulfonated [see Schmidt, R.;Weis, W.; Klingmuller, V.; Staudinger, H. J.; Z. Klin. Chem., 1967, 5,308] derivative have been introduced in clinical chemistry for theestimation of Fe²⁺.

In general these oligopyridines are high melting products and aredifficult to dissolve in the usual organic solvents. These factors havesomewhat restricted their further development. According to the presentinvention, a versatile, direct synthesis of a variety of substitutedpyridines and oligopyridines is described, which compounds havefavorable solubility characteristics.

In particular the invention discloses hitherto unknown pyrylium andthiopyrylium, and a method of preparing the same.

SUMMARY OF THE INVENTION

This invention relates to a convenient and practical synthesis of avariety of pyrylium (where X is oxygen), and consequently thiopyrylium(X is sulfur) and seleninium (X is selenium) salts of general formula I:##STR2## Where R¹ and R² represent an alkyl radical such as methyl,having up to about 15 carbon atoms, either in a normal or branchedchain; an aromatic group such as a phenyl radical, or substituted phenylradical having, as substituents, alkyl radicals with from 1 to about 15carbon atoms, alkoxy radicals having 1 to about 4 carbon atoms,substituted amino radicals have 1 or 2 carbon radicals and containing 1to about 4 carbon atoms; a heterocyclic group such as pyridine orsubstituted pyridine radical having, as substituents, alkyl radicalswith 1 to about 15 carbon atoms, alkoxy radicals having 1 to about 4carbon atoms, and amino radicals having 1 or 2 carbon radicalscontaining 1 to about 4 carbon atoms, as well as thiophene radicals andfuran radicals. R³ represents thioalkyl radical having 1 to about 4carbon atoms, thiobenzyl, thioaryl and thiocycloalkyl radicals, as wellas thioheteryl radicals such as 2-thiopylidyl and related 5- and6-membered systems.

Z is an anionic function including such ions as tetrafluorborate,perchlorate, methanesulfonate, and halogeno ions such as bromide,iodide, chloride, fluoride and the like.

Another object of the invention is to provide a novel class of compoundswhich are used as sensitisers for photosensitive systems and whichproduce a marked increase in sensitivity at longer wavelengths of thevisible light spectrum.

A further object of the invention is to provide marked versatility inthe substituents incorporated into these pyrylium salts and at the sametime provide a direct and efficient synthesis of these salts.

In particular, these pyrylium and thiopyrylium salts are prepared by anovel method involving the steps of: condensing a methyl ketone withcarbon disulfide in the presence of sodium hydride; treating theresulting product with methyl iodide to form theα-oxoketenedithioacetal; condensing the α-oxoketenedithioacetal withanother methyl ketone in the presence of two equivalents of potassiumtert-butoxide to form a 1,5-enedione; and cyclizing the enedione withtetrafluoroboric acid.

Other strong bases like potassium tert-butoxide, sodium or potassiumhydroxide may be used to generate the enolate of the methyl ketone forreaction with carbon disulfide and a variety of non-protic solvents,such as dimethylformamide, dimethylsulfoxide, toluene, benzene, etc. ormixtures of these solvents may be used. Alkylation of thedi-thiocarboxylate di-anion occurs readily with a variety of alkylhalides or dialkyl sulfates.

An additional novel feature of the reaction is the use of twoequivalents of potassium tert-butoxide in the formation of the1,5-enedione, resulting in its isolation as its potassium salt withsubsequent conversion into the neutral product. This greatly facilitatesthe ease of isolation of the 1,5-enedione as well as suppresses sidereactions.

In this novel preparation of pyrylium salts, two methods may beutilized. In the first method, the 1,5-enedione is actually isolatedprior to cyclization and in the second method, generation of the1,5-enedione and ring closure to the pyrylium salts are actually carriedout sequentially in one reaction vessel.

The various features of novelty which characterize the invention arepointed out with particularity in the claims annexed to and forming apart of this disclosure. For a better understanding of this invention,its operating advantages and specific objects attained by its uses,reference is made to the accompanying descriptive material in whichpreferred embodiments of the invention are illustrated.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to one embodiment of the invention, the method used is a"one-pot", two component procedure involving the in situ generation ofunsaturated 1,5-diketones derived by a reaction ofα-ketoketenedithioacetals and methyl ketone carbanions. Examples shownin Table I. Reaction of these enediones with ammonium acetate in hotacetic acid gives 2,6-disubstituted-4-methylthiopyridines having generalformula G. A representative selection of examples of this procedure, isshown in the Table II. Alternatively, the 1,5-enedione may be isolatedbefore conversion into the pyridine although, in general, this offers noadvantages over the more direct procedure. The synthesis of2,2',2"-terpyridinyl (product C in reaction I where R═R¹ ═2--C₅ H₄ N; R²═H; X═N) illustrates the general procedure used. In Table I the SCH₃group can alternately be the groups designated R₃ above.

    TABLE I      ##STR3##        1,5-Enediones Derived from α-Oxoketene Dithioacetals Analysis     Substituent  Yield Crystal M..sup.+ Calcd Found .sup.ν CO. R.sub.1     R.sub.2 Mp °C. % Habit Mol Formula Rel Int C H N C H N cm.sup.-1  H     ' NMR (CDCl.sub.3) δ       C.sub.6 H.sub.5 C.sub.6 H.sub.5 106-108 76 Pale Yellow C.sub.18     H.sub.16 O.sub.2 S 296 (7) 72.96 5.44  72.82 5.41  1680, 8.20-7.34 (m,     10, aromatic), 6.82 (s, 1, CH), 4.64     Prisms         1630 (s, 2,     CH.sub.2), 2.59 (s, 3, SCH.sub.3)     (Benzene/     Pet. Ether) C.sub.6     H.sub.5 2-C.sub.4 H.sub.3 S 116-118 61 Pale Yellow C.sub.16 H.sub.14     O.sub.2 S.sub.2 302 (8) 63.57 4.67 63.54 4.79 1700, 8.10-7.06 (m, 8,     aromatic), 6.82 and 6.70 (s, 1, CH),     Needles         1680, 4.62 and     4.60 (s, 2, CH.sub.2), 2.54 (s, 3, SCH.sub.3)     (Benzene/1645,     Pet. Ether)1625 C.sub.6 H.sub.5 2-C.sub.5 H.sub.4 N 124-125 58 Colorless     C.sub.17 H.sub.15 NO.sub.2 S 248 (2) 68.67 5.08 4.71 68.57 5.194.391680,     8.63 (br, d, 1 aromatic), 8.20-7.33 (m, 8, aromatic), 7     Needles        1640 6.76 (s, 1, CH), 4.76, 4.60 (s, 2, CH.sub.2), 2.43     (Cyclohexa     ne)          (s, 3, SCH.sub.3) 2-C.sub.4 H.sub.3 S 2-C.sub.4 H.sub.3 S     164-165 70Pale Yellow C.sub.14 H.sub.12 O.sub.2 S.sub.3 308 (7) 54.55     3.92 54.80 4.06 1670, 7.96-7.03 (m, 6, aromatic), 6.70 (s, 1, CH), 4.60        Prisms         1620 (s, 2, CH.sub.2) 2.50 (s, 3, SCH.sub.3)     (Benzene) 2-C.sub.4 H.sub.3 O 2-C.sub.4 H.sub.3 S 140-142 47 Pale Yellow     C.sub.14 H.sub.12 O.sub.3 S.sub.2  292 (11) 57.54 4.14 57.78 4.20 1690,     7.90-6.96 (m, 5, aromatic), 6.73 and 6.66 (s, 1, CH),     Needles      1670 6.50 (m, 1, aromatic), 4.55 and 4.45 (s, 2, CH.sub.2), 2.47     (Benzene/         1640, (s, 3, SCH.sub.3)     Pet. Ether)   1620     2-C.sub.5 H.sub.4 N 2-C.sub.5 H.sub.4 N 120-122 13 Pale Yellow C.sub.16     H.sub.14 N.sub.2 O.sub.2 S 298 (1) 64.42 4.73 9.39 64.42 4.84 9.37 1700,     8.74-7.20 (m, 9, aromatic and vinylic), 4.83 (s, 2,     Prisms     1646 CH.sub.2), 2.60 (s, 3, SCH.sub.3)     (Pet. Ether) 2-C.sub.5     H.sub.4 N 2-C.sub.4 H.sub.3 S 102-104 60 Colorless C.sub.15 H.sub.13     NO.sub.2 S.sub.2 303 (1) 59.40 4.32 4.62 59.67 4.51 4.72 1700, 8.85-6.96     (m, 7, aromatic), 7.70 and 6.70 (s, 1, CH),     Prisms         1630 4.80     and 4.57 (s, 2, CH.sub.2), 2.56 and 2.51 (s, 3,     (Benzene/   SCH.sub.3     )     Cyclohexane) 3-BrC.sub.6 H.sub.4 3-BrC.sub.6 H.sub.4 118-119 81     Colorless C.sub.18 H.sub.14 Br.sub.2 O.sub.2 S 454 (3) 47.60 3.11 47.59     3.14 1690, 8.15-7.15 (m, 8, aromatic), 6.22 (s, 1, CH),     Needles        1640 4.48 (s, 2, CH.sub.2), 2.50 (s, 3, SCH.sub.3)     (Methanol)     4-CH.sub.3 OC.sub.6 H.sub.4 4-CH.sub.3 OC.sub.6 H.sub.4 159-161 100     Yellow C.sub.20 H.sub.20 O.sub.4 S  356 (20) 67.40 5.66 67.38 5.66 1655     8.03, 7.91, 7.0, 6.90 (4d, 8, J = 9.0 Hz, aromatic), 7.0     Needles          (s, 1, CH), 4.22 (s, 2, CH.sub.2), 3.90 and     (Benzene)     3.85 (2s, 6, OCH.sub.3), 2,30 (s, 3, SCH.sub.3) 4-CH.sub.3 OC.sub.6     H.sub.4 CH.sub.3 106-107 42 Colorless C.sub.14 H.sub.16 O.sub.3 S  264     (18) 63.61 6.10 63.70 6.13 1710, 8.02, 7.96, 7.15 (3d, 4, J = 9.0 Hz,     aromatic),     Needles         1640 6.77, 6.13 (s, 1, CH), 4.45, 3.93     (s, 2, CH.sub.2),     (Methanol/          3.88 (s, 3, OCH.sub.3),     Ether)2.49, 2.41 (s, 3, SCH.sub.3), 2.34, 2.18 (s, 3, CH.sub.3).     2-C.sub.4 H.sub.3 S 5-Cl2-C.sub.4 H.sub.2 S 134-134.5 75 Pale Yellow     C.sub.14 H.sub.11 ClO.sub.2 S.sub.3  342 (10) 49.04 3.23 49.27 3.35     1665, 7.82-6.50 (m, 4, thiophene), 6.63, 6.53 (s, 1, CH),     Prisms         1623 4.53, 4.43 (s, 2, CH.sub.2), 2.45 (s, 3, SCH.sub.3)     (Benzene) 5-Br2-C.sub.4 H.sub.2 S 5-Br2-C.sub.4 H.sub.2 S 125-126.5 97     Pale Yellow C.sub.14 H.sub.10 Br.sub.2 O.sub.2 S.sub.3 464 (7)36.06 2.16     36.25 2.13 1669, 7.52, 7.39, 7.06, 6.98, (4d, 4, J=4.0 Hz, thiophene),       Prisms        1620 6.48 (s, 1, CH), 4.40 (s, 2, CH.sub.2), 2.47 (s,     (Ethanol)   3, SCH.sub.3)     ##STR4##

                  TABLE II                                                        ______________________________________                                        Substituted Pyridines Derived from α-Ketoketenedithioacetals (A)                                MP       Yield                                        R          R.sup.1      °C.                                                                             %      M.sup.+a                              ______________________________________                                        C.sub.6 H.sub.5                                                                          C.sub.6 H.sub.5                                                                            105-107  81     277                                   4-CH.sub.3 OC.sub.6 H.sub.4                                                              CH.sub.3     69-70    70     .sup. 245.sup.b                       4-BrC.sub.6 H.sub.4                                                                      4-BrC.sub.6 H.sub.4                                                                        115-116  85     435                                   4-CH.sub.3 OC.sub.6 H.sub.4                                                              4-CH.sub.3 OC.sub.6 H.sub.4                                                                90.5-91  48     337                                   C.sub.6 H.sub.5                                                                          2-C.sub.5 H.sub.4 N                                                                        80-81    89     278                                   2-C.sub.5 H.sub.4 N                                                                      2-C.sub.5 H.sub.4 N                                                                        120-121  81     279                                   2-C.sub.5 H.sub.4 N                                                                      2-C.sub.4 H.sub.3 S                                                                        133-134  80     284                                   6-Br--2-C.sub.5 H.sub.3 N                                                                6-Br--2-C.sub.5 H.sub.3 N                                                                  184-185  31     437                                   2-C.sub.4 H.sub.3 S                                                                      2-C.sub.4 H.sub.3 S                                                                        115-116  99     289                                   2-C.sub.4 H.sub.3 S                                                                      5-Cl--2-C.sub.4 H.sub. 2 S                                                                 115-116  72     323                                   2-C.sub.4 H.sub.3 O                                                                      2-C.sub.4 H.sub. 3 O                                                                       96-97    64     257                                   2-C.sub.4 H.sub.3 O                                                                      2-C.sub.4 H.sub.3 S                                                                        95-97    74     273                                   ______________________________________                                         .sup.a Relative Intensities, 100%, .sup.b 93%.                           

As generally shown in reaction I, 2-Acetylpyridine (R═2--C₅ H₄ N) wasconverted into 3,3-bis(methylthio)-1-(2-pyridinyl)-2-propen-1-one(product A where; R═2--C₅ H₄ N) using NaH/DMSO, CS₂ and CH₃ I and wasobtained as yellow needles (71%) from ethanol, m.p. 108°-109° C., ν_(CO)1605 cm⁻¹, M.⁺ 225. This α-ketoketenedithioacetal (3.0 g, 0.013 mol) wasadded to a solution of 2-acetylpyridine (1.6 g, 0.013 mol) andpostassium tert-butoxide (3.0 g, 0.027 mol) in dry THF (80 mL). Afterstirring for 3 hours at room temperature, ammonium acetate (10.0 g,0.013 mol) and glacial acetic acid (80 mL) were added to the abovesolution which was then heated for 2 hours with continuous removal ofTHF. After cooling, addition of ice-water resulted in the separation of2,6-di(2'-pyridinyl)-4-(methylthio)pyridine (Product C where; R═R¹═2--C₅ H₄ N; R² ═SCH₃ ; X═N) which crystallized from ethanol:water ascolorless needles, 2.0 g (79%), m.p. 120°-121° C., M.⁺ 279. Refluxingthis product with an excess of Raney nickel (6 hr) in ethanol gave2,2',2"-terpyridinyl (Product C where; R═R¹ ═2--C₅ H₄ N; R² ═H; X═N) ascream prisms (60%), m.p. 84°-85° C., M.⁺ 233.2735 (100%).

This reaction sequence is also useful for pyridine ring annulation to avariety of cycloalkyl ketones. Reaction of Product A where R═4--CH₃ OC₆H₄, with cyclohexanone under the above conditions gave Product D (X═N)as colorless needles (10%), m.p. 105°-106° C., M.⁺ 285 (100%). Inaddition quinquepyridine may also be obtained by this route. Reactioncompound E (3.0 g, 0.013 mol) with 2-acetylpyridine (1.09 g, 0.0066 mol)and potassium tert-butoxide (3.0 g, 0.027 mol) in dry THF as above, gave2,6-bis[2'-(4'-methylthio)-6'-(2"-pyridinyl)pyridinyl]pyridine (ProductF as colorless flakes from DMF: 1.5 g (53%), mp 265°-266° C., M.⁺479.6271 (100%). ##STR5##

According to the invention, these 1,5-enediones provide a ready entryinto a variety of substituted pyrylium salts. This new procedureovercomes the majority of the disadvantages of current procedures Z* andapproaches the goal of a general synthesis.

This is illustrated by the preparation of2-methyl-4-methylthio-6-(4-methoxyphenyl)pyrylium tetrafluoroborate(Product C where; R═4--CH₃ OC₆ H₄ ; R¹ ═CH₃ ; R² ═SCH₃ ; X═O⁺.BF-₄).Potassium tert-butoxide (5.04 g, 0.045 mol) was added to a stirredmixture of the potassium salt of acetone (1.2 g, 0.02 mol) and theketenedithioacetal (Product A where R═4--CH₃ OC₆ H₄ ; 5.0 g, 0.02 mol).An initial yellow suspension changed over a 16 hour reaction period intoa dense green precipitate of Product B (R═4--CH₃ OC₆ H₄ ; R¹ ═CH₃). Thiswas collected and added to an ice-cold 4% HCl solution (200 mL) givingthe corresponding 1,5-diketone as a thick suspension which was collectedand then stirred in dichloromethane (40 mL) with HBF₄ (20 mL of 48%solution) for 4 hours at 50° C.

The yellow pyrylium salt separated during this period and, afteraddition of water (20 mL) the pyrylium salt was collected. Itcrystallized from acetic acid as light yellow needles (70%) m.p.207°-210° C. decom. Use of cyclohexanone as the ketonic component in theabove reaction gave2-(4-methoxyphenyl)-4-methylthio-5,6,7,8-tetrahydrobenzopyryliumtetrafluoroborate (Product D X═O⁺.BF₄) as yellow-green needles (40%)from acetic acid, m.p. 245°-250° C. decomp. Aromatic substituents werereadily introduced into the 2,6-positions e.g., use of4-methoxyacetophenone (as starting compound in I where; R¹ ═4--CH₃ OC₆H₄) in the above reaction gave2,6-bis(4-methoxyphenyl)-4-(methylthio)pyrylium tetrafluoroborate(C;R═R¹ ═4--CH₃ OC₆ H₄ ; R² ═SCH₃ ; X═O⁺.BF-₄) as yellow prisms (53%)from acetic acid, m.p. 288°-290° C. decomp. In some cases the yieldapproaches quantitive as in the formation of 2,6-diphenyl-4-(methlthio)pyrylium tetrafluoroborate (C;R═R¹ ═C₆ H₅ ; R² ═SCH₃ ;X═O⁺.BF-₄) which was isolated as pale-green needles (93%) from1,2-dichloroethane, mp 253°-255° C. The variety of aryl and heterocyclicketones, either as the α-ketoketenedithioacetal component or the ketoniccomponent, which take part in this reaction allows the introduction of awide variety of substituents in the 2- and 6-positions. See Rastogi, R.R.; Kumar, A., Ila, H., Junjappa, H. J. Chem. Soc. Perkin I 1978, 549;Thuillier, A.; Vialle, J. Bull Soc. Chim. France 1962, 2182, 2187;Thuillier, A., Vialle, J. Bull. Soc. Chim. France 1962 2194

Alternatively, this synthesis may be accomplished in a "one-pot"reaction. In this case, the 1,5-diketone is not isolated and thetetrafluoroboric acid is merely added to the initial THF reactionmixture. The product is contaminated with KBF₄ which may be removed bywashing with hot water, resulting in a reduced yield of the pyryliumsalt. This procedure is best with aromatic substituents in the 2- and6-positions. The 4-methylthio group in C (X═O⁺.BF-₄) similarly to the4-chloro and 4-methoxy groups, is susceptible to displacement bynucleophiles such as secondary amines. See R. M. Ankee and A. H. Cook,J. Chem. Soc. 1946, 117; L. C. King and F. J. Ozog, J. Org. Chem. 1955,20, 448.

This synthesis offers many advantages over those currently used for rhepreparation of the corresponding 4-(substitutedthio)pyrylium salts. Aspyrylium salts of the corresponding 1,5-diketones are readily convertedinto thiopyrylium and seleninium salts, these ring systems are nowreadily available with similarly diverse substitution patterns.

A more detailed version of equation I is shown at equation II that moreclearly indicates the reaction scheme of the invention. ##STR6##

The three stage reaction which yields products A, B and C respectivelyis as follows:

Preparation of 3,3-Bis(methylthio)-1-phenyl-2-propen-1-one(Product A)

Acetophenone (6.0 g, 0.05 mol) was mixed with sodium hydride (4.2 g of57% oil suspension, 0.1 mol), carbon disulfide (6.0 g, 0.075 mol), MeI(22.5 g, 0.15 mol) and dry benzene (80 mL) Dimethylacetamide was addeddropwise (10 mL) while cooling and the mixture was stirred overnight atroom temperature. Crushed ice was then added to the benzene solutionwith care (unreacted NaH might be present), the benzene extract wasdried (MgSO₄) and evaporated under reduced pressure to give pale yellowcrystals. Crystallization from methanol gave pale yellow needles: 6.0 g(58%) m.p. 90°-92° C. (lit. m.p. 93° C.); IR (KBr)ν_(CO) 1600 cm⁻¹ ; NMR(CDCl₃)δ7.9-7.5 (m, 5, aromatic), 6.76 (s,1, vinylic) 2.56 (s, 3,SCH₃),2.52 (s,3, SCH₃). See A. Thuiller and J. Vialle, Bull. Soc. Chem. Fr.1959, 1398.

Preparation of 1,5-Diphenyl-3-methylthiopent-2-en-1,5-dione (Product B)

Ketene dithioacetal (Product A) (2.0 g, 0.0089 mol) was added to asolution of acetophenone (1.07 g, 0.0089 mol) and potassiumtert-butoxide (2.0 g, 0.0178 mol) in dry THF (20 mL). The temperature ofthe reaction mixture was raised to 60° C. and the mixture was stirredfor 1 hour during which time an orange-red precipitate formed. This wascollected and added to an ice-cold HCl solution (4% acid) and the oilymaterial which separated allowed to crystallize. The brown solid wascollected and recrystallized from benzene: petroleum ether (b.p.80°-100° C.) from which it separated as pale-yellow prisms: 1.8 g (70%),m.p. 106°-108° C.: IR (KBr)ν_(CO) 1680, 1630 cm⁻¹ ; NMR (CDCl₃)δ8.0-7.56(m, 10, aromatic), 6.82 (s,1, vinylic), 4.64 (s,2,CH₂), 2.59 (s,3,SCH₃);M.⁺ 296 (7%).

Anal. Calcd for C₈ H₁₆ O₂ S; C,72.96; H,5.44. Found: C,72.82; H,5.41.

Preparation of 2,6-Diphenyl-4-methylthiopyrylium Tetrafluoroborate(Product C)

The above pentendione (Product B) (3.5 g, 0.012 mol) was dissolved in1,2-dichloroethane (30 mL), tetrafluoroboric acid (20 mL of 48%solution) was added and the mixture heated under reflux for 30 minutes.After cooling to room temperature, the green crystals were collected andthe mother liquor was refluxed for an additional 30 minutes, yielding afurther amount of product on cooling: 4.0 g (93%). It crystallized from1,2-dichloroethane as pale green needles, m.p. 253°-255° C.: IR (KBr)1601 (C═O⁺) cm⁻¹ ; NMR (CF₃ COOH)δ8.0-7.5 (m, 10, aromatic); δ2.97(s,3,SCH₃); M.⁺ 279 (74%).

Anal. Calcd for C₁₈ H₁₅ OS.BF₄ : C, 59.03; H, 4.12. Found: C, 59.16, H,4.18.

The following additional examples are disclosed for a betterunderstanding of the invention:

EXAMPLE 1 Preparation of 2,6-Diphenyl-4-(methylthio)pyryliumTetrafluoroborate

3,3-Bis(methylthio)-1-phenyl-2-propen-1-one, prepared by the methoddescribed by A. Thuillier and J. Vialle, Bull. Chim. Soc. France, page1398 (1959) and also by I. Shahak and Y. Sasson, Tetrahedron Letters,page 4207 (1973), (2.0 g, 0.0089 mol) was added to a solution ofacetophenone (1.07 g, 0.0089 mol) and potassium tert-butoxide (2.0 g,0.0178 mol) in dry THF (20 ml). The solution was stirred overnight atroom temperature and the resultant red-brown precipitate was collectedand added to an ice-cold HCl solution (4% acid) and the oily materialthat separated was allowed to crystallize from benzene:petroleum ether(b.p. 80°-100° C.) from which1,5-diphenyl-3-methylthio-2-penten-1,5-dione separated as pale yellowprisms: 2.0 g (76%), m.p. 106°-108° C.; IR (KBr)ν_(CO) 1680, 1630 cm⁻¹ ;λmax (CH₃ OH) nm (log ε) 319 (4.19), 241 (4.22); NMR (CDCl₃) 8.20-7.34(m, 10, aromatic), 6.82 (s, 1, vinylic), 4.64 (s,2,CH₂), 2,59 (s, 3,SCH₃) M.⁺ 296 (17).

Anal. Calcd for C₁₈ H₁₆ O₂ S: C, 72.96; H, 5.44. Found: C, 72.82; H,5.41.

This 1,5-enedione (3.50 g, 0.0118 mol) was added to a solution oftetrafluoroboric acid (20 ml of 48% aqueous solution) and1,2-dichloroethane (30 ml) and the mixture heated under reflux for 30minutes. After cooling to room temperature, the green crystals werecollected and the mother liquor was refluxed for an additional 30minutes, yielding further product on cooling.

Recrystallization from 1,2-dichloroethane afforded2,6-diphenyl-4-(methylthio)pryrylium tetrafluoroborate as pale greenneedles: 4.0 g (93%), m.p. 253°-255° C.; IR (KBr) 1601 (C═O⁺)cm⁻¹, λmax(CH₃ OH nm (log ε) 336 (3.89) 266 (4.02); NMR (CF₃ COOH 8.0-7.50 (m, 12,aromatic), 3.0 (s, 3, SCH₃); M.⁺ (C₁₈ H₁₅ OS) 279 (74).

Anal. Calcd for C₁₈ H₁₅ BF₄ OS: C, 59.03; H, 4.12. Found: C, 59.16; H,4.18.

EXAMPLE 2

2,6-Di-(4-methoxyphenyl)-4-(methylthio)pyrylium Tetrafluoroborate3,3-Bis(methylthio)-1-(4-methoxyphenyl)-2-propen-1-one (4.0 g, 0.02mol), prepared by the method of I. Shahak and Y. Sasson, TetrahedronLetters, page 4207 (1973), was added to a stirred mixture of potassiumtert-butoxide (5.04 g, 0.045 mol.) and 4-methoxyacetophenone (3.0 g,0.02 mol.) in freshly distilled THF (50 ml). The resulting bright orangesuspension was stirred at room temperature for 8 hours. The solid wasthen collected by filtration and added to ice-cold hydrochloric acid (4%aqueous solution). The orange oil that initially separated rapidlysolidified. The enedione was collected and dissolved in1,2-dichloroethane (25 ml). Tetrafluoroboric acid (5 ml, 48%) was addedand the mixture heated under reflux for 30 minutes. After cooling theorange solid was collected and yellow prisms were obtained oncrystallization from dichloroethane: 4.5 g (53%), m.p. 288°-290° C.(decomp); NMR (DMSO-d₆)δ3.0 (s, 3, SCH₃), 3.88 (s, 6, OCH₃), 7.27 (d,4J=9.0Ha), 8.30 (d,4,J=9.0H₃), 8.32 (s,2, aromatic).

Anal. Calcd for C₂₀ H₂₉ O₃ SBF₄ : C, 56.35; H, 4.49. Found: C, 56.20; H,4.52.

EXAMPLE 3 2-Methyl-4-methylthio-6-(4-methoxyphenyl)pyryliumTetrafluoroborate

To a stirred solution of3,3-bis(methylthio)-1-(4-methoxyphenyl)-2-propen-1-one (10.0 g, 0.042mol) prepared by the method described by I. Shahak and Y. Sasson,Tetrahedron Letters, page 4207 (1973), and acetone (2.4 g, 0.043 mol) infreshly distilled THF was added potassium tert-butoxide (10.1 g, 0.09mol). The thick green mixture was stirred at room temperature overnight.The potassium salt was then collected and added to iced water (150 ml).This suspension was stirred with gradual addition of hydrochloric acid(4%) until a cream precipitate formed.1-(4-Methoxyphenyl)-3-methylthio-2-hexen-1,5-dione was collected andrecrystallized from methanol diethyl ether giving colorless needles: 4.6g (42%), m.p. 105°-107° C.;

IR(KBr)ν_(CO) 1710, 1640 cm⁻¹ ; M.⁺ 264 (18).

Anal. Calcd for C₁₄ H₁₆ O₃ S: C, 63,61; H,6.10. Found: C, 63.70; H,6.13.

To a solution of this 1-(4-methoxyphenyl)-3-methylthio-2-hexen-1,5-dione(2.0 g, 7.57 mmol) in 1,2-dichloroethane (20 ml) was addedtetrafluoroboric acid (10 ml, 48%). The mixture was stirred for fourhours at 50° C. during which time a dense yellow solid formed. Afteraddition of water (25 ml) and filtration, crystallization from aceticacid gave pale yellow needles of 2-methyl-4-methylthio6-(4-methoxyphenyl)pyrylium tetrafluoroborate: 2.2 g (87%), m.p.207°-210° C. (decomp), IR (KBr)ν_(CO) +1625 cm⁻¹ ; NMR(DMSO-d₆)δ8.34(s,1, aromatic), 8.29 (d,2, J=9.0 Hz, aromatic), 7.80 (br. 3, 1,aromatic), 7.18 (d, 2, J=9.0 Hz, aromatic) 3.97 (s, 3, OCH₃), 2.91 (s,3, SCH₃), (s, 3, CH₃); M.⁺ 246 (100).

Anal. Calcd for C₁₄ H₁₅ O₂ SBF₄ : C, 50.32; H, 4.53. Found: C, 50.12; H,4.55.

EXAMPLE 44-Methylthio-2-(4-methoxyphenyl)-5,6,7,8-tetrahydrobenzo[b]pyryliumTetrafluoroborate

To a stirred mixture of potassium tert-butoxide (10.1 g, 0.09 mol) andcyclohexanone (3.90 g 0.04 mol) in freshly distilled THF was added3,3-bis(methylthio)-1-(4-methoxyphenyl)-2-propen-1-one (10.0 g, 0.039mol) prepared as described above. The mixture rapidly became very deepred and was stirred overnight. Addition of the cooled reaction mixtureto ice cold hydrochloric acid (200 ml, 4%) gave a yellow precipitatethat was collected and washed with ice cold THF before further use (7.3g, 62%). Crystallization from ethanol gave yellow prisms withconsiderable decomposition: mp. 189°-10-° C. (decomp).

The unpurified enedione (5.0 g, 0.0164 mol) was stirred in1,2-dichloroethane (30 ml) together with tetrafluoroboric acid (20 ml,48%). The mixture was stirred at room temperature over a period of fivehours during which it became orange. Addition of water (25 ml) andfiltration gave a yellow solid that crystallized from acetic acid asyellow needles: 4.05 g (74%), m.p. 246°-250° C. (decomp): NMR(DMSO-d₆)δ8.42 (s,1, aromatic), 8.62 (d, 2, J=9.0 Hz, aromatic), 7.55(d,2, J=9.0 Hz, aromatic), 4.22 (s, 3, OCH₃), 3.27, 2.78, 2.20 (br. s,8, cyclohexyl).

Anal. Calcd for C₁₇ H₁₉ O₂ SBF₄ : C, 54.65; H, 5.12. Found: C, 54.12; H,5.10.

EXAMPLE 5 General Procedure for the Preparation of2,6-Disubstituted-4-(methylthio)thiopyrylium Salts

To a solution of the corresponding pyrylium tetrafluoroborate (0.003mol) in acetone (60 ml), sodium sulfide monohydrate (0.015 mo in water(10 ml) was added slowly. The solution was stirred for one hour, apurple color developing during this time. Tetrafluoroboric Acid (10 mlof a 48% aqueous solution) was added and the reaction mixture stirredfor two additional hours. The brown precipitate was collected andrecrystallized from acetic acid.

Using this procedure, 2,6-diphenyl-4-(methylthio)thiopyryliumtetrafluoroborate was obtained in 73% yield, m.p. 230°-232° C. (decomp)after crystallization from acetic acid from which it separated as brownneedles; λmax (CH₃ OH) nm (log ε) 358 (3.99), 296 (3.93), 239 (4.35),225 (4.35); NMR (CF₃ COOH)δ8.4 (s,2, aromatic), 8.27-7.62 (m, 10,aromatic), 3.0 (s,3, SCH₃); M.⁺ (C₁₈ H₁₅ BF₄ S₄) 382 (7).

Anal. Calcd for C₁₈ H₁₅ BF₄ S₂ : C, 56.56; H, 3.95. Found C, 56.17; H,3.97.

Similarly, 2,6-di-(4-methoxyphenyl)-4-(methylthio)thiopyryliumtetrafluoroborate is obtained in 48% yield, m.p. 198-200 C, as fineorange needles after crystallization from acetic acid; NMR("Unisol")δ8.30 (s, 2, aromatic), 8.02 (d, 4, J=9.0 Hz aromatic), 7.18(d, 4, J=9.0 Hz, aromatic), 3.95 (s, 3, OCH₃), 3.02 (s, 3, SCH₃).

Anal. Calcd for C₂₀ H₁₈ BF₄ O₂ S₂ : C, 54.31; H, 4.33. Found: C, 53.99;H, 4.40.

While specific embodiments of the invention have been shown anddescribed in detail to illustrate the application of the principles ofthe invention, it will be understood that the invention may be embodiedotherwise without departing from such principles.

What is claimed is:
 1. A method of preparing a salt having the generalformula: ##STR7## where X is oxygen; R¹ and R² represent a branched orunbranched alkyl radical chain up to 15 carbon atoms; an aromatic groupoptionally substituted by alkyl radicals with from 1 to about 15 carbonatoms, alkoxy radicals having 1 to about 4 carbon atoms, or substitutedamino radicals with 1 to 2 carbon radicals containing 1 to about 4carbon atoms; a heterocyclic group optionally substituted by alkylradicals with about 1 to 15 carbon atoms, alkoxy radicals having from 1to about 4 carbon atoms or substituted amino radicals having 1 to 2carbon radicals containing 1 to about 4 carbon atoms; 3-bromo phenyl;5-chloro-2-thienyl; or 5-bromo-2-thienyl;R³ is a thioalkyl radical withfrom 1 to about 4 carbon atoms, thiobenzyl, thioaryl, thiocycloalkylradicals and thioheteryl radicals; and Z⁻ is an anionic function; themethod comprising: condensing a methyl ketone with a carbon disulfide inthe presence of sodium hydride; treating the resulting product withalkyl halides or alkyl sulfate containing about 1 to 4 carbon atoms, toform α-oxoketenedithioacetal; condensing the α-oxoketenedithioacetalwith the same or another methyl ketone in the presence of twoequivalents of a strong base to form a 1,5-enedione with an acid of theanionic function to form a salt.
 2. A method according to claim 1,wherein the alkyl halide comprises methyl iodide.
 3. A method accordingto claim 1, wherein said methyl ketone comprises acetophenone.
 4. Amethod according to claim 1, wherein the two equivalents of a strongbase comprise two equivalents of potassium tert-butoxide.
 5. A methodaccording to claim 1, including conducting the steps of the method in anon-protic solvent.
 6. A method according to claim 5, wherein thenon-protic solvent is at least one of, dimethylformamide,dimethylsulfoxide, toluene and benzene.
 7. A method according to claim1, wherein said alkyl halide is substituted by a dialkyl sulfate.
 8. Amethod according to claim 1, including isolating said 1,5-enedione priorto recyclizing the enedione with tetrafluoroboric acid.
 9. A methodaccording to claim 1, comprising cyclizing said 1,5-enedione after it iscondensed in a single reaction vessel.
 10. A method according to claim1, wherein Z⁻ is one of tetrafluoroborate, perchlorate, methanesulfonateand halogeno ions.
 11. A method according to claim 1, wherein said acidof the anionic function comprises tetrafluoroboric acid.